There have been known a variety of ink-jet recording devices for ejecting ink droplets onto a sheet substrate to reproduce an image thereon. To print a high quality image in a short period of time using such ink-jet recording device, it has been understood that a tone reproduction in which a plurality sizes of ink dots are deposited on the sheet substrate is effective. For this toner reproduction, an ink-jet recording device including two types of nozzles, i.e., large size nozzles and small size nozzles, are proposed in the art.
The technique is useful to some extend, however, a variation range of diameters of the dots formed on the sheet substrate is restricted. This in turn restricts a tone reproduction range by the recording device. In particular, for a printing of the halftone image such as picture to which a greater tone reproductivity has been required, the known technique could not provide a satisfactory tone gradation. Also, for ejecting small and large ink droplets, the technique needs both small diameter nozzles and large diameter nozzles to be formed in a head portion of the device, which renders the device costly.
Another ink-jet recording device is known in the art in which a plurality of ink materials having different colors of different properties, respectively, are deposited on the same place to superimpose the dots of different colors for the purpose of reproducing a colorful image on the sheet substrate. In such full color ink-jet printer, the ink droplets of different colors ejected on the same ejecting condition are desired to have a certain diameter. However, because each of the color ink materials has independent property, it is unavoidable that the ink droplets ejected under the same ejecting condition have different diameters. One possible method to overcome this problem is to provide nozzles of different sizes for respective colors, but this increases the cost of the recording device as described above.